Developer with experience with HEROKU and GIT needed ASAP please

Hello, I have a new client that has a PHP website hosted in HEROKU. I have access to Heroku but I have no idea how to access website files. I also understand the website code is in GIT, but I am also unfamiliar with this. I only need someone to educate me on how this works, I need to provide my SEO developer with access to the website so he can begin work but I do not know how these systems work (I don't think its FTP/ admin). I will pay you for 1 or 2 hours of your time, or less, all I need is an answer as to how I can give my SEO developer access so he can begin work. I greatly appreciate your help and feedback. Thank you and I look forward to your bids.